All-terrain vehicles are one kind of straddle type vehicle, so called because they have a straddle seat that supports at least one rider sitting in a straddle fashion. These vehicles have generally, although not necessarily, four wheels contacting the ground and supporting the vehicle via a suspension. An engine, supported by the frame, is operatively connected to at least one of the wheels to propel the vehicle. Handlebars are typically pivotally connected to the frame in front of the straddle seat and are operatively connected to the front wheels to steer the vehicle. Fenders and fairings offer protection for the rider against projectiles from the wheels when the vehicle is in motion.
As their name would suggest, all-terrain vehicles are designed to travel over various types of terrain. To that end, they are generally equipped with low pressure tires (i.e. “balloon tires” generally having a pressure less than 138 kilopascal (or 20 psi) which have a large contact patch with the ground. This large contract patch reduces the pressure exerted on the ground by the tire. This low pressure applied on the ground is advantageous for these vehicles as it allows them to go over soft terrain like mud, sand or snow.
Particularly with reference to snow-covered terrain, these balloon tires are not an always optimal as on snow it becomes increasingly difficult for the vehicle to move when the thickness of snow on the ground becomes significant. This is so because, depending on the snow conditions, it may happen that pressure applied on the snow surface by even the balloon tires becomes too great to support the vehicle. The tires thus begin to sink in the snow. The further the tires sink into the snow the more likely that the lower portion of the frame of the vehicle will come into contact with the snow surface. This situation is not at all desirable as when the frame touches the snow on the ground it begins to direct transfers the load of the vehicle onto the snow surface. Friction between the frame and the snow on the ground creates drag when the vehicle moves. The pressure provided on the ground by the tires progressively diminishes and traction may be subsequently lost in favor of greater contact between the lower portion of the frame and the ground.
Moreover, the wheels have less traction when the drag increases and their friction with the snow surface diminishes. The tires begin to slip over the ground surface while the vehicle becomes more and more supported by the frame contacting directly the snow on the ground, until the tires completely loose traction on the snow—the vehicle is then struck.
An alternative known in the art provides an replacing the wheels with an endless belt system (or track systems) when the vehicle is to be used in snowy conditions. Many types of such systems exist. For example, some endless belt systems have been designed to be added over the wheels of an all-terrain vehicle. Sometimes the addition of either a number of additional wheels or a track supporting structure is required to be added to the existing vehicle. Other endless belt systems have been designed to completely replace the wheels.
Replacement of the wheels by endless belt systems provides a larger contact area (patch) on the ground compared to size of the contact area (patch) of a wheel on the ground—even with a low pressure balloon tire. Floatation over the snow is increased and the lower portion of the frame is maintained at a greater distance from the snow surface. The vehicle can be used in deeper snow because floatation and traction are preserved.
These systems, while good, are not without their drawbacks. For one, the size of the contact patch also affects the ease of steering the vehicle. On a wheeled or tracked vehicles, the wheels that steer the vehicle are turned about a pivot point on the ground (more precisely over the steering axis) based on the steering geometry of the vehicle. The contact area of the wheel or track that surrounds the pivot point on the ground of the steering wheels opposes, via friction, the rotational movement of the wheel or track about this pivot point. Thus, the larger the contact area on the ground the more area there is to generate friction which opposed the movement about the pivot point, and the tougher it is to rotate the patch around the pivot point. Therefore, the larger contact area on the ground generated by an endless belt system inherently increases the force needed to steer the vehicle.
Another difficulty is that some endless belt systems are fixedly connected to the frame of the vehicles. This prevents the systems from tracking the shape of the uneven terrain over which the vehicle is traveling. In prior art systems that are pivotally attached the to frame, in the past, they have always been pivotally attached about what would have been the hub of the wheel if a wheel had been attached. This means that the system must have rather large movements in order to track the shape of the terrain, which is still not optimal. In other type of system, the traction provided is thus somewhat limited because the contact area of the endless belt is not capable of adapting to the ground's imperfections.
Finally, normally these endless belt systems are used on vehicles that were designed to accommodate wheels. These belt systems are sold typically in the aftermarket by those other than the original equipment manufacturers. Thus, the suspension, drive train, steering linkages, etc. have all been designed to sustain the loads generated by wheels, and not necessarily by belt systems. Belt systems typically generate higher mechanical loads as they are heavier than wheels and require more force in order to steer. In some circumstances, on some vehicles, improvement is required in order to sustain such loads.
Accordingly, there remains a need for an improved endless belt system for vehicles, and particularly all-terrain vehicles, which ameliorates some of the deficiencies associated with prior art systems.